JP6929089B2

JP6929089B2 - Image forming device

Info

Publication number: JP6929089B2
Application number: JP2017045253A
Authority: JP
Inventors: 浩之福原
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2017-03-09
Filing date: 2017-03-09
Publication date: 2021-09-01
Anticipated expiration: 2037-03-09
Also published as: JP2018149681A

Description

本発明は、シート等の記録媒体上に画像を形成する、例えば、レーザプリンタ、複写機、ファクシミリ等の画像形成装置に関する。 The present invention relates to an image forming apparatus such as a laser printer, a copier, or a facsimile, which forms an image on a recording medium such as a sheet.

電子写真方式の画像形成装置に用いられる光学走査装置は、光源から出射される画像データに応じた光束を回転多面鏡で偏向して走査レンズを透過させ、これにより、感光体の表面を光のスポットで走査・露光することで、感光体に潜像を形成する。走査レンズは、所謂、ｆθ特性を有するレンズである。ｆθ特性とは、回転多面鏡が等角速度で回転しているときに、スポットが感光体の表面上を等速で走査するようにする光学的特性である。 The optical scanning device used in the electrophotographic image forming device deflects a light beam corresponding to the image data emitted from the light source by a rotating polymorphic mirror to transmit the scanning lens, whereby the surface of the photoconductor is exposed to light. A latent image is formed on the photoconductor by scanning and exposing at the spot. The scanning lens is a lens having a so-called fθ characteristic. The fθ characteristic is an optical characteristic that causes the spot to scan on the surface of the photoconductor at a constant velocity when the rotating multifaceted mirror is rotating at a constant angular velocity.

光学走査装置を小型化するため、回転多面鏡の近くにｆθ特性を有する走査レンズを配置しようとすると、走査レンズの厚みが厚くなり、かつ、その形状が複雑化し、樹脂では成形が困難となる。そこで、光学走査装置の小型化のため、走査レンズを使用しない、或いは、ｆθ特性を有さない走査レンズを使用することが考えられている。特許文献１は、光学走査装置が形成する光のスポットが感光体の表面を等速で走査しない場合でも、感光体の表面上に形成されるドット間の距離及びドット幅が一定になるよう、画像形成のためのクロック信号の周波数を変更することを開示している。 If an attempt is made to arrange a scanning lens having fθ characteristics near a rotating polymorphic mirror in order to reduce the size of the optical scanning device, the thickness of the scanning lens becomes thick and the shape becomes complicated, which makes molding difficult with resin. .. Therefore, in order to reduce the size of the optical scanning device, it is considered that a scanning lens is not used or a scanning lens having no fθ characteristic is used. Patent Document 1 states that the distance between dots and the dot width formed on the surface of the photoconductor are constant even when the spot of light formed by the optical scanning device does not scan the surface of the photoconductor at a constant speed. It discloses that the frequency of the clock signal for image formation is changed.

特開昭５８−１２５０６４号公報Japanese Unexamined Patent Publication No. 58-125064

しかしながら、特許文献１は、画像の形成開始位置については何ら開示していない。特許文献１では、曲線的に変化する実際の走査速度に対し、クロック信号の周波数を線形的に補正しているため、クロック信号の周波数が、走査速度の変化を補正するための周波数とは一致しない部分が生じる。このため、実際の形成開始位置と、クロック信号のカウント数により計算される形成開始位置が一致せず画像品質が低下し得る。 However, Patent Document 1 does not disclose any image formation start position. In Patent Document 1, since the frequency of the clock signal is linearly corrected with respect to the actual scanning speed that changes in a curve, the frequency of the clock signal matches the frequency for correcting the change in the scanning speed. There is a part that does not. Therefore, the actual formation start position and the formation start position calculated by the count number of the clock signal do not match, and the image quality may deteriorate.

本発明は、潜像の形成開始位置のずれを抑えることができる画像形成装置を提供するものである。 The present invention provides an image forming apparatus capable of suppressing a shift in the starting position of forming a latent image.

本発明の一態様によると、画像形成装置は、感光体と、クロック信号を生成する生成手段と、前記生成手段が生成する前記クロック信号に応じた画像データに基づき駆動される光源と、前記感光体に前記画像データに応じた潜像を形成するため、前記光源が射出する光を偏向して前記感光体を走査する偏向手段であって、前記感光体を走査する前記光の走査速度が像高に応じて変化する、前記偏向手段と、前記感光体に形成する前記潜像の形成開始位置を判定する判定手段と、前記生成手段が生成する前記クロック信号の周波数を制御する制御手段と、を備えており、前記制御手段は、１つの走査線の走査において、前記形成開始位置より上流側の第１位置においては、前記形成開始位置に応じて決定される基準周波数となる様に前記クロック信号の周波数を制御し、前記形成開始位置より下流側の前記画像データに応じた潜像を形成するための第２位置においては、前記感光体の像高と前記生成手段が生成する前記クロック信号の周波数との関係を示す周波数情報により示される周波数となる様に前記クロック信号の周波数を制御し、前記制御手段は、前記周波数情報が示す前記形成開始位置に対応する像高の周波数に基づき前記基準周波数を決定することを特徴とする。 According to one aspect of the present invention, the image forming apparatus includes a photoconductor, a generation means for generating a clock signal, a light source driven based on image data corresponding to the clock signal generated by the generation means, and the photosensitivity. In order to form a latent image corresponding to the image data on the body, it is a deflection means for deflecting the light emitted by the light source to scan the photoconductor, and the scanning speed of the light scanning the photoconductor is an image. The deflection means, which changes according to the height, the determination means for determining the formation start position of the latent image formed on the photoconductor, and the control means for controlling the frequency of the clock signal generated by the generation means. The control means has the clock so that, in scanning one scanning line, the first position on the upstream side of the formation start position has a reference frequency determined according to the formation start position. At the second position for controlling the frequency of the signal and forming a latent image corresponding to the image data on the downstream side of the formation start position, the image height of the photoconductor and the clock signal generated by the generation means are used. The frequency of the clock signal is controlled so as to be the frequency indicated by the frequency information indicating the relationship with the frequency of the above, and the control means is based on the frequency of the image height corresponding to the formation start position indicated by the frequency information. It is characterized by determining a reference frequency.

本発明によると、潜像の形成開始位置のずれを抑えることができる。 According to the present invention, it is possible to suppress the deviation of the formation start position of the latent image.

一実施形態による画像形成装置の構成図。The block diagram of the image forming apparatus by one Embodiment. 一実施形態による光学走査装置の構成図。The block diagram of the optical scanning apparatus according to one Embodiment. 一実施形態による像高と部分倍率の関係を示す図。The figure which shows the relationship between the image height and a partial magnification by one Embodiment. 一実施形態による像高とクロック信号の周波数比率の関係を示す図。The figure which shows the relationship between the image height and the frequency ratio of a clock signal by one Embodiment. 図４及び図７の一部の拡大図。Enlarged view of a part of FIGS. 4 and 7. 一実施形態によるクロック信号の周波数の推移を示す図。The figure which shows the transition of the frequency of the clock signal by one Embodiment. クロック信号の周波数の推移とシートサイズとの関係を示す図。The figure which shows the relationship between the frequency transition of a clock signal and a sheet size. 一実施形態による制御部のブロック図。A block diagram of a control unit according to an embodiment. 一実施形態によるシートサイズと基本周波数の関係を示す図。The figure which shows the relationship between the sheet size and the fundamental frequency by one Embodiment. 一実施形態による基準周波数から周波数情報に基づく周波数への切替の説明図。An explanatory diagram of switching from a reference frequency according to an embodiment to a frequency based on frequency information.

以下、本発明の例示的な実施形態について図面を参照して説明する。なお、以下の実施形態は例示であり、本発明を実施形態の内容に限定するものではない。また、以下の各図においては、実施形態の説明に必要ではない構成要素については図から省略する。 Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. The following embodiments are examples, and the present invention is not limited to the contents of the embodiments. Further, in each of the following figures, components that are not necessary for the description of the embodiment will be omitted from the drawings.

図１は、画像形成装置Ｄ１の断面図である。画像形成装置Ｄ１は、像担持体である感光体１０３を備えたプロセスカートリッジ１０２と、光学走査装置Ｓ１と、を備えている。画像形成時、感光体１０３は回転駆動され、かつ、プロセスカートリッジ１０２内の図示しない帯電部により一様な電位に帯電される。光学走査装置Ｓ１は、画像データに基づいた光束を射出し、これにより、感光体１０３を走査・露光して感光体１０３上に画像データに応じた潜像を形成する。感光体１０３に形成された潜像は、プロセスカートリッジ１０２内の図示しない現像部によってトナーにより現像され、トナー像として顕像化される。一方、給紙カセット１０４に収容されたシートＰは、給送ローラ１０５によって１枚ずつ分離されながら給送され、搬送ローラ１０６によって、さらに下流側に搬送される。転写ローラ１０９は、感光体１０３上に形成されたトナー像を、シートＰに転写する。トナー像が形成されたシートＰは、定着部１１０に向けて搬送される。定着部１１０は、シートＰを加熱・加圧して、トナー像をシートＰに定着させる。その後、シートＰは、排出ローラ１１１によって外部に排出される。 FIG. 1 is a cross-sectional view of the image forming apparatus D1. The image forming apparatus D1 includes a process cartridge 102 including a photoconductor 103 which is an image carrier, and an optical scanning apparatus S1. At the time of image formation, the photoconductor 103 is rotationally driven and charged to a uniform potential by a charged portion (not shown) in the process cartridge 102. The optical scanning device S1 emits a luminous flux based on the image data, thereby scanning and exposing the photoconductor 103 to form a latent image corresponding to the image data on the photoconductor 103. The latent image formed on the photoconductor 103 is developed with toner by a developing unit (not shown) in the process cartridge 102, and is visualized as a toner image. On the other hand, the sheets P housed in the paper feed cassette 104 are fed while being separated one by one by the feed roller 105, and further downstream by the transport roller 106. The transfer roller 109 transfers the toner image formed on the photoconductor 103 to the sheet P. The sheet P on which the toner image is formed is conveyed toward the fixing portion 110. The fixing unit 110 heats and pressurizes the sheet P to fix the toner image on the sheet P. After that, the sheet P is discharged to the outside by the discharge roller 111.

図２は、光学走査装置Ｓ１の構成を示す斜視図である。光源１１２が出射した光束Ｌは、アナモフィックコリメータレンズ１１３によって主走査断面内では略平行光とされ、副走査断面内では収束光とされる。なお、略平行光とは、弱収束光および弱発散光を含む。次に、光束Ｌは、開口絞り１１４を通って光束幅が制限されて、回転多面鏡１１５の反射面においてほぼ線像（主走査方向が長手となる線像）として結像する。この光束Ｌは、回転多面鏡１１５の反射面で反射される。ここで、回転多面鏡１１５を一定の角速度で回転させることによって、光束Ｌの反射方向は変更され、これにより、光束Ｌは、偏向走査される。光束Ｌは、回転多面鏡１１５での反射方向によっては、ビームディテクト（以下、ＢＤと表記する。）センサ１１９に入射する。ＢＤセンサ１１９は、光束Ｌの検出タイミングを、ＢＤ信号として、制御部２００（図８）に出力する。なお、光束Ｌの検出タイミングは、主走査方向の書き出し位置、つまり潜像の形成開始位置の同期検出タイミングでもある。また、光束Ｌは、回転多面鏡１１５での反射方向によっては、走査光として走査レンズ１１７を透過し、感光体１０３の表面にスポットを形成する。走査レンズ１１７は結像光学素子である。 FIG. 2 is a perspective view showing the configuration of the optical scanning device S1. The luminous flux L emitted by the light source 112 is regarded as substantially parallel light in the main scanning cross section and converged light in the sub scanning cross section by the anamorphic collimator lens 113. The substantially parallel light includes weakly convergent light and weakly divergent light. Next, the luminous flux L is imaged as a substantially line image (a line image whose main scanning direction is longitudinal) on the reflecting surface of the rotating polymorphic mirror 115, with the luminous flux width limited through the aperture diaphragm 114. This luminous flux L is reflected by the reflecting surface of the rotating multifaceted mirror 115. Here, by rotating the rotating multifaceted mirror 115 at a constant angular velocity, the reflection direction of the luminous flux L is changed, whereby the luminous flux L is deflected and scanned. The luminous flux L is incident on the beam detect (hereinafter referred to as BD) sensor 119 depending on the reflection direction of the rotating multi-sided mirror 115. The BD sensor 119 outputs the detection timing of the luminous flux L as a BD signal to the control unit 200 (FIG. 8). The detection timing of the luminous flux L is also the synchronous detection timing of the writing position in the main scanning direction, that is, the starting position of forming the latent image. Further, the luminous flux L passes through the scanning lens 117 as scanning light depending on the reflection direction of the rotating multifaceted mirror 115, and forms a spot on the surface of the photoconductor 103. The scanning lens 117 is an imaging optical element.

回転多面鏡１１５の回転によって光束Ｌを偏向走査し、感光体１０３上で光束Ｌによる主走査が行われる。感光体１０３は、画像形成時、円筒の軸線周りに回転駆動され、これにより副走査が行われる。このようにして感光体１０３の表面には画像データに応じた潜像が形成される。 The luminous flux L is deflected and scanned by the rotation of the rotating multi-sided mirror 115, and the main scanning by the luminous flux L is performed on the photoconductor 103. At the time of image formation, the photoconductor 103 is rotationally driven around the axis of the cylinder, whereby sub-scanning is performed. In this way, a latent image corresponding to the image data is formed on the surface of the photoconductor 103.

本実施形態において、走査レンズ１１７は、所謂、ｆθ特性を有するものではない。ｆθ特性を有する走査レンズでは、光学走査装置Ｓ１の小型化のために回転多面鏡１１５に近接して配置しようとすると、その形状が複雑かつ厚肉となり樹脂による成形が困難となる。よって、ｆθ特性を有する走査レンズを用いる場合は回転多面鏡との距離を一定以上離す必要がある。それに対して、ｆθ特性を有さない走査レンズ１１７はレンズ形状が単純であり、樹脂の成形性も良くなるため樹脂成型に適している。その結果、走査レンズ１１７を回転多面鏡１１５に近接して配置することが可能になり、更には主走査方向の幅を小さくすることができる。その結果、光学走査装置の小型化を実現できる。 In the present embodiment, the scanning lens 117 does not have the so-called fθ characteristic. In a scanning lens having an fθ characteristic, if an attempt is made to place the scanning lens close to the rotating multifaceted mirror 115 in order to reduce the size of the optical scanning device S1, the shape becomes complicated and thick, and molding with a resin becomes difficult. Therefore, when using a scanning lens having fθ characteristics, it is necessary to keep a certain distance from the rotating multifaceted mirror. On the other hand, the scanning lens 117 having no fθ characteristic is suitable for resin molding because the lens shape is simple and the moldability of the resin is improved. As a result, the scanning lens 117 can be arranged close to the rotating multi-sided mirror 115, and the width in the main scanning direction can be reduced. As a result, the optical scanning device can be downsized.

本実施形態に係る走査レンズ１１７の走査特性は、以下の式（１）で表される。
Ｙ＝（Ｋ／Ｂ）ｔａｎ(Ｂθ) （１）
式（１）において、θは走査レンズ１１７の光軸方向に対する走査角度であり、Ｙは走査角度θで偏向された光束の感光体１０３上での主走査方向の集光位置（像高）である。なお、以下では、光軸上の像高（Ｙ＝０、θ＝０）を軸上像高と呼び、軸上像高以外の像高を軸外像高と呼ぶものとする。さらに、軸外像高の最大値、つまり、走査角度θが最大（最大走査画角）となる時の像高を最軸外像高と呼ぶものとする。また、上記式（１）において、Ｋは軸上像高における結像係数であり、Ｂは走査レンズ１１７の走査特性を決定するための係数（以下、走査特性係数と呼ぶ。）である。 The scanning characteristics of the scanning lens 117 according to this embodiment are represented by the following equation (1).
Y = (K / B) tan (Bθ) (1)
In the formula (1), θ is the scanning angle of the scanning lens 117 with respect to the optical axis direction, and Y is the condensing position (image height) of the luminous flux deflected by the scanning angle θ on the photoconductor 103 in the main scanning direction. be. In the following, the image height on the optical axis (Y = 0, θ = 0) is referred to as an on-axis image height, and an image height other than the on-axis image height is referred to as an off-axis image height. Further, the maximum value of the off-axis image height, that is, the image height when the scanning angle θ becomes the maximum (maximum scanning angle of view) is referred to as the most off-axis image height. Further, in the above equation (1), K is an imaging coefficient at the axial image height, and B is a coefficient for determining the scanning characteristic of the scanning lens 117 (hereinafter, referred to as a scanning characteristic coefficient).

結像係数Ｋは、走査レンズ１１７に平行光が入射する場合の走査特性（ｆθ特性）Ｙ＝ｆθにおけるｆに相当する係数である。すなわち、結像係数Ｋは、走査レンズ１１７に平行光以外の光束が入射する場合に、ｆθ特性と同様に集光位置Ｙと走査角度θとを比例関係にするための係数である。 The imaging coefficient K is a coefficient corresponding to f at scanning characteristic (fθ characteristic) Y = fθ when parallel light is incident on the scanning lens 117. That is, the imaging coefficient K is a coefficient for making the focusing position Y and the scanning angle θ proportional to each other when a light flux other than parallel light is incident on the scanning lens 117, similar to the fθ characteristic.

走査特性係数について補足すると、Ｂ＝０の時の式（１）は、Ｙ＝Ｋθとなるため、従来の光学走査装置に用いられる結像レンズの走査特性Ｙ＝ｆθに相当する。また、Ｂ＝１の時の式（１）は、Ｙ＝Ｋｔａｎθとなるため、撮像装置（カメラ）などに用いられるレンズの射影特性Ｙ＝ｆ・ｔａｎθに相当する。すなわち、式（１）において、走査特性係数Ｂを０≦Ｂ≦１の範囲で設定することで、射影特性Ｙ＝ｆ・ｔａｎθと、ｆθ特性であるＹ＝ｆθとの間の走査特性を得ることができる。 Supplementing the scanning characteristic coefficient, the equation (1) when B = 0 is Y = Kθ, which corresponds to the scanning characteristic Y = fθ of the imaging lens used in the conventional optical scanning apparatus. Further, since the equation (1) when B = 1 is Y = Ktanθ, it corresponds to the projection characteristic Y = f · tanθ of a lens used in an imaging device (camera) or the like. That is, in the equation (1), by setting the scanning characteristic coefficient B in the range of 0 ≦ B ≦ 1, the scanning characteristic between the projection characteristic Y = f · tan θ and the fθ characteristic Y = fθ is obtained. be able to.

ここで、式（１）を走査角度θで微分すると、次式（２）に示すように走査角度θに対する感光体１０３上での光束Ｌの走査速度が得られる。
ｄＹ／ｄθ＝Ｋ／（ｃоｓ^２（Ｂθ））（２） Here, when the equation (1) is differentiated by the scanning angle θ, the scanning speed of the luminous flux L on the photoconductor 103 with respect to the scanning angle θ can be obtained as shown in the following equation (2).
dY / dθ = K / (cоs ² (Bθ)) (2)

さらに、式（２）を軸上像高における速度ｄＹ／ｄθ＝Ｋで除し、軸上像高の走査速度に対する各軸外像高の走査速度のずれ量(部分倍率)で表現すると、次式（３）に示すようになる。
１／（ｃоｓ^２（Ｂθ））−１＝ｔａｎ^２（Ｂθ）（３）
このように、本実施形態において、光学走査装置Ｓ１は、Ｂ＝０の以外では、軸上像高と軸外像高とで光束の走査速度が異なる。 Further, when equation (2) is divided by the velocity dY / dθ = K at the on-axis image height and expressed by the deviation amount (partial magnification) of the scanning speed of each off-axis image height with respect to the scanning speed of the on-axis image height, it is expressed as follows. It becomes as shown in the formula (3).
1 / (cоs ² (Bθ)) -1 = tan ² (Bθ) (3)
As described above, in the present embodiment, the optical scanning apparatus S1 has different scanning speeds of the luminous flux between the on-axis image height and the off-axis image height except for B = 0.

図３は、像高と部分倍率との関係の一例を示している。本実施形態では、図３に示す様に、軸上像高から軸外像高に向かうにつれて徐々に走査速度が速くなるため部分倍率が大きくなる。たとえば、最軸外像高での部分倍率が３０％であると、軸上像高と同じ時間だけ光照射した場合、最軸外像高では、感光体１０３への主走査方向の照射長が軸上像高での１．３倍となる。 FIG. 3 shows an example of the relationship between the image height and the partial magnification. In the present embodiment, as shown in FIG. 3, the scanning speed gradually increases from the on-axis image height to the off-axis image height, so that the partial magnification increases. For example, if the partial magnification at the most off-axis image height is 30%, when light is irradiated for the same time as the on-axis image height, the irradiation length of the photoconductor 103 in the main scanning direction is at the most off-axis image height. It is 1.3 times the on-axis image height.

図４は、主走査方向の１つのライン（走査線）における像高とクロック信号の周波数比率との関係を示している。なお、周波数比率とは、軸上像高における理想的なクロック信号の周波数を基準とした各像高での周波数の比である。図４の点線は、ｆθ特性を有さない走査レンズ１１７を使用することによる走査速度の変化を補正するための理想的な周波数比率を示している。一方、図４の実線は、実際に使用する周波数比率を示している。本実施形態では、主走査方向を９つの区間に分割し、各区間内では周波数が線形的に変化する様にクロック信号の周波数を設定する。なお、図４のａからｋは、各区間の境界である。なお、各境界におけるクロック信号の周波数は理想値に一致させる。画像形成装置に各区間の境界の周波数を記憶させておくことで、画像形成装置は、区間内のクロック信号の周波数を、当該区間の境界の周波数を線形補間することで求めることができる。 FIG. 4 shows the relationship between the image height and the frequency ratio of the clock signal in one line (scanning line) in the main scanning direction. The frequency ratio is the ratio of the frequencies at each image height based on the frequency of the ideal clock signal at the axial image height. The dotted line in FIG. 4 shows an ideal frequency ratio for correcting a change in scanning speed due to the use of a scanning lens 117 having no fθ characteristic. On the other hand, the solid line in FIG. 4 shows the frequency ratio actually used. In the present embodiment, the main scanning direction is divided into nine sections, and the frequency of the clock signal is set so that the frequency changes linearly within each section. In addition, a to k of FIG. 4 are boundaries of each section. The frequency of the clock signal at each boundary matches the ideal value. By storing the frequency of the boundary of each section in the image forming apparatus, the image forming apparatus can obtain the frequency of the clock signal in the section by linearly interpolating the frequency of the boundary of the section.

図５（Ａ）は、図４の一部を拡大した図である。上述した様に、境界ａと境界ｂに対応する像高での周波数は理想的なものであり、理想的な主走査方向の幅を持つドットが形成される。しかしながら、連続曲線である実際の部分倍率に対し、クロック信号の周波数を線形近似するため、区間内では理想的な周波数との誤差が生じる。たとえば、境界ａと境界ｂとの中間付近では、実際の部分倍率よりクロック信号の周波数が速いため、ドット間隔およびドット自体が縮んで形成され、所謂、補正残差が生じる。 FIG. 5A is an enlarged view of a part of FIG. As described above, the frequency at the image height corresponding to the boundary a and the boundary b is ideal, and dots having an ideal width in the main scanning direction are formed. However, since the frequency of the clock signal is linearly approximated to the actual partial magnification which is a continuous curve, an error from the ideal frequency occurs in the interval. For example, in the vicinity of the middle between the boundary a and the boundary b, the frequency of the clock signal is faster than the actual partial magnification, so that the dot spacing and the dots themselves are shrunk to form a so-called correction residual.

図６は、１ラインの走査を行う際のクロック信号の周波数の推移を示している。なお、ＢＤＯ信号とは、図８を用いて後述するように、ＢＤセンサ１１９が出力するＢＤ信号に基づき生成される信号であり、ＢＤ信号と同様に、走査光の位置を示す信号である。また、ＶＤＯ信号とは、画像データに対応する信号である。ＢＤＯ信号の受信タイミングから、潜像形成領域の走査方向における上流側の端部（潜像の形成開始位置）に走査光が到達するまでの期間において、画像形成装置は、クロック信号の周波数を変化させず、一定の値（以下、基準周波数と呼ぶ。）とする。そして、走査光が形成開始位置、或いは、その上流側の近傍に到達すると、クロック信号の周波数を、走査速度の変化を補正する様にその像高に応じて変化させる。そして、走査光が潜像形成領域の走査方向における下流側の端部(形成終了位置)に到達すると、画像形成装置は、クロック信号の周波数を、例えば、基準周波数に固定する。画像形成装置は、これを走査線毎に繰り返して画像を形成する。 FIG. 6 shows the transition of the frequency of the clock signal when scanning one line. The BDO signal is a signal generated based on the BD signal output by the BD sensor 119, as will be described later with reference to FIG. 8, and is a signal indicating the position of the scanning light, like the BD signal. The VDO signal is a signal corresponding to image data. The image forming apparatus changes the frequency of the clock signal in the period from the reception timing of the BDO signal to the arrival of the scanning light at the upstream end (latent image formation start position) in the scanning direction of the latent image forming region. It is not allowed to be set to a constant value (hereinafter referred to as a reference frequency). Then, when the scanning light reaches the formation start position or the vicinity on the upstream side thereof, the frequency of the clock signal is changed according to the image height so as to correct the change in the scanning speed. Then, when the scanning light reaches the downstream end (formation end position) of the latent image forming region in the scanning direction, the image forming apparatus fixes the frequency of the clock signal to, for example, a reference frequency. The image forming apparatus repeats this for each scanning line to form an image.

図７は、シートのサイズと、部分倍率と、クロック信号の周波数比率との関係を説明する図である。画像形成装置は、様々なサイズのシートに対して画像形成を行う。例えば、レター（ＬＴＲ）、Ａ４、Ｂ５サイズのシートや、封筒などの小サイズのシートに対しても画像形成を行う。画像形成対象のシートのサイズが変わると、潜像の形成開始位置もそれに応じて変わる。そして、形成開始位置が異なると、実際の形成開始位置が目標位置よりずれることが生じ得る。つまり、シートの左端の余白が要求と異なることになり得る。例えばＡ４サイズのシートでは、図５（Ｂ）の、網掛け領域の積分量だけの補正残差が発生して、左端の余白が目標値より狭くなる。本実施形態では、このような画像の形成開始位置のずれを抑制する。 FIG. 7 is a diagram illustrating the relationship between the sheet size, the partial magnification, and the frequency ratio of the clock signal. The image forming apparatus forms an image on sheets of various sizes. For example, an image is formed on a letter (LTR), A4, B5 size sheet, or a small size sheet such as an envelope. When the size of the sheet to be image-formed changes, the position where the latent image starts to be formed also changes accordingly. Then, if the formation start position is different, the actual formation start position may deviate from the target position. That is, the margin on the left edge of the sheet can be different from the requirement. For example, in an A4 size sheet, a correction residual corresponding to the integrated amount of the shaded area as shown in FIG. 5B is generated, and the margin at the left end becomes narrower than the target value. In the present embodiment, such deviation of the image formation start position is suppressed.

図８は、画像形成装置Ｄ１の制御部２００のブロック図を示している。ＣＰＵ２０１は、画像形成装置Ｄ１の全体の制御を行う。駆動制御部２０２は、ＢＤ信号２０７に基づいて、各走査の同期タイミングを示すＢＤＯ信号２１２を画像信号生成部２０３に出力するとともに、回転多面鏡１１５の回転を制御する回転駆動信号２０８を光学走査装置Ｓ１に出力する。上述した様に、ＢＤ信号２０７は、感光体１０３の外側にあるＢＤセンサ１１９が回転多面鏡１１５で反射した光を受信したタイミングを示している。ＢＤＯ信号２１２は、ＢＤ信号２０７が示す光の検出タイミングと同じ、或いは、ＢＤ信号２０７が示す光の検出タイミングから所定の時間だけ遅れたタイミングを示す信号である。ＢＤＯ信号２１２が示すタイミングに基づき、画像信号生成部２０３は、回転多面鏡１１５で反射した光が、感光体１０３の走査方向の２つの端部のうちの上流側の端部に到達するタイミングを判定することができる。また、画像信号生成部２０３は、回転多面鏡１１５で反射した光が、感光体１０３の走査方向における潜像の形成開始位置に到達するタイミングを判定することができる。なお、本実施形態において、潜像の形成領域のサイズ並びに潜像の形成開始位置及び形成終了位置は、シートのサイズに応じて決定されるものとする。つまり、本実施形態では、ユーザが設定する余白量は、潜像の形成領域内であるが、トナーを付着させない領域とし、潜像の形成開始位置及び形成終了位置は、ユーザが設定する余白量に拘らずシートのサイズにより決まるものとする。 FIG. 8 shows a block diagram of the control unit 200 of the image forming apparatus D1. The CPU 201 controls the entire image forming apparatus D1. Based on the BD signal 207, the drive control unit 202 outputs a BDO signal 212 indicating the synchronization timing of each scan to the image signal generation unit 203, and optically scans the rotation drive signal 208 that controls the rotation of the rotary multifaceted mirror 115. Output to device S1. As described above, the BD signal 207 indicates the timing at which the BD sensor 119 on the outside of the photoconductor 103 receives the light reflected by the rotating multifaceted mirror 115. The BDO signal 212 is a signal indicating the same timing as the light detection timing indicated by the BD signal 207, or a timing delayed by a predetermined time from the light detection timing indicated by the BD signal 207. Based on the timing indicated by the BDO signal 212, the image signal generation unit 203 determines the timing at which the light reflected by the rotating multifaceted mirror 115 reaches the upstream end of the two ends in the scanning direction of the photoconductor 103. It can be determined. Further, the image signal generation unit 203 can determine the timing at which the light reflected by the rotating multifaceted mirror 115 reaches the latent image formation start position in the scanning direction of the photoconductor 103. In this embodiment, the size of the latent image formation region and the latent image formation start position and formation end position are determined according to the size of the sheet. That is, in the present embodiment, the margin amount set by the user is within the latent image formation region, but the area is not to adhere the toner, and the latent image formation start position and formation end position are the margin amount set by the user. Regardless, it shall be determined by the size of the sheet.

画像信号生成部２０３は、演算部２０４と記憶部２０５と、を備えている。記憶部２０５は、ｆθ特性を有さない走査レンズ１１７を使用することによる走査速度の像高による変化を補償・補正するための周波数情報を保持している。周波数情報は、図４を用いて説明した様に、像高とクロック信号の周波数との関係を示す情報である。より詳しくは、本実施形態では、図４に示す様に、１つのラインを、走査方向において複数の区間に分割し、区間毎に周波数を線形近似したもの、つまり、走査速度の像高による変化を補正するための理想的な周波数の近似値を画像形成に使用する。さらに、記憶部２０５は、画像形成対象のシートのサイズ並びに潜像の形成開始位置及び形成終了位置と、クロック信号の基準周波数との関係を示す基準情報も保持している。図７を用いて説明したように、基準周波数は、潜像形成領域に走査光が到達するまでのクロック信号の周波数である。 The image signal generation unit 203 includes a calculation unit 204 and a storage unit 205. The storage unit 205 holds frequency information for compensating / correcting a change in the scanning speed due to the image height due to the use of the scanning lens 117 having no fθ characteristic. The frequency information is information indicating the relationship between the image height and the frequency of the clock signal, as described with reference to FIG. More specifically, in the present embodiment, as shown in FIG. 4, one line is divided into a plurality of sections in the scanning direction, and the frequency is linearly approximated for each section, that is, the change due to the image height of the scanning speed. An approximation of the ideal frequency to correct is used for image formation. Further, the storage unit 205 also holds reference information indicating the relationship between the size of the sheet to be image-formed, the formation start position and formation end position of the latent image, and the reference frequency of the clock signal. As described with reference to FIG. 7, the reference frequency is the frequency of the clock signal until the scanning light reaches the latent image forming region.

画像信号生成部２０３は、ＢＤＯ信号２１２が示すタイミングとシートのサイズとに基づき、感光体１０３上において走査光が潜像の形成開始位置に到達するタイミングを判定する。なお、画像信号生成部２０３は、ＢＤＯ信号２１２が示すタイミングから、走査光が潜像の形成開始位置に到達するタイミングまでの期間を、生成した基準周波数のクロック信号によりカウントして判定する。そして、走査光が潜像の形成開始位置に到達するタイミングに合わせて画像データであるＶＤＯ信号２１１を出力する。なお、このＶＤＯ信号２１１は、画像信号生成部２０３が生成する周波数情報に基づくクロック信号に同期したものである。画像信号生成部２０３は、走査光が潜像形成領域内を走査している間、周波数情報に基づき、走査光の像高に応じた周波数のクロック信号を生成して、これに同期したＶＤＯ信号２１１を駆動制御部２０２に出力する。なお、ＣＰＵ２０１が出力するＴＯＰ信号２１０は、１つのシートへの画像形成開始タイミングを示すものである。 The image signal generation unit 203 determines the timing at which the scanning light reaches the latent image formation start position on the photoconductor 103 based on the timing indicated by the BDO signal 212 and the size of the sheet. The image signal generation unit 203 counts and determines the period from the timing indicated by the BDO signal 212 to the timing when the scanning light reaches the latent image formation start position by counting the generated reference frequency clock signal. Then, the VDO signal 211, which is image data, is output at the timing when the scanning light reaches the latent image formation start position. The VDO signal 211 is synchronized with the clock signal based on the frequency information generated by the image signal generation unit 203. The image signal generation unit 203 generates a clock signal having a frequency corresponding to the image height of the scanning light based on the frequency information while the scanning light is scanning in the latent image forming region, and the VDO signal synchronized with the clock signal is generated. 211 is output to the drive control unit 202. The TOP signal 210 output by the CPU 201 indicates the timing of starting image formation on one sheet.

駆動制御部２０２は、ＣＰＵ２０１からの制御信号と、画像信号生成部２０３からのＶＤＯ信号２１１に基づいて、光源１１２を駆動するための光源駆動信号２０９を光学走査装置Ｓ１に出力する。光学走査装置Ｓ１の光源１１２は、光源駆動信号２０９に基づき射出する光をオン・オフして感光体１０３に潜像を形成する。 The drive control unit 202 outputs a light source drive signal 209 for driving the light source 112 to the optical scanning device S1 based on the control signal from the CPU 201 and the VDO signal 211 from the image signal generation unit 203. The light source 112 of the optical scanning apparatus S1 turns on / off the light emitted based on the light source drive signal 209 to form a latent image on the photoconductor 103.

図９は、本実施形態によるシート毎の基準周波数を示しいている。図９では、５つのシートの種別それぞれに対応する、基準周波数ＡからＥの５つの基準周波数を設けている。画像信号生成部２０３は、画像形成対象のシートのサイズを図示しないホストコンピュータからの画像形成コマンドや、ユーザ入力に基づき判定し、判定したシートのサイズに対応する基準周波数のクロック信号を生成する。また、画像信号生成部２０３は、判定したシートのサイズに対応する基準周波数のクロック信号で、ＢＤＯ信号２１２から潜像の形成開始位置までのカウント数を判定する。そして、画像信号生成部２０３は、判定したカウント数に達すると、駆動制御部２０２にＶＤＯ信号２１１を出力する。 FIG. 9 shows a reference frequency for each sheet according to the present embodiment. In FIG. 9, five reference frequencies A to E are provided corresponding to each of the five sheet types. The image signal generation unit 203 determines the size of the sheet to be image-formed based on an image formation command from a host computer (not shown) or user input, and generates a clock signal having a reference frequency corresponding to the determined sheet size. Further, the image signal generation unit 203 determines the number of counts from the BDO signal 212 to the latent image formation start position with the clock signal of the reference frequency corresponding to the determined sheet size. Then, when the determined count number is reached, the image signal generation unit 203 outputs the VDO signal 211 to the drive control unit 202.

本実施形態では、図９に示す様に、各シートに対応する基準周波数を、周波数情報が示す各シートの形成開始位置でのクロック信号の周波数に一致させる。そして、図１０（Ａ）に示す様に、走査光が形成開始位置５０に到達するまでは、画像信号生成部２０３は基準周波数のクロック信号を生成する。走査光が潜像の形成開始位置に到達した後、潜像を形成している間、画像信号生成部２０３は、周波数情報が示す周波数となる様にクロック信号の周波数を制御する。なお、走査光が潜像の形成終了位置に到着後、画像信号生成部２０３は基準周波数のクロック信号を生成する。形成開始位置までは基準周波数のクロック信号でカウントするため、補正残差を生じさせることなく、書き出し位置を高い精度で維持することが可能となる。また、図９に示す様に、周波数情報における区間境界を、シートの潜像形成領域の走査方向の端部に一致するように設けることができる。これにより、基準周波数は、画像形成対象のシートの潜像の形成開始位置において走査速度の変動を補正するための周波数に一致し、よって、更に、潜像の形成開始位置の精度を高めることができる。なお、周波数情報に従い、像高に応じてクロック信号の周波数を変化させる制御の開始時に電気的な遅延が発生する場合には、走査光が形成開始位置に到達するタイミングより少し前から周波数情報に基づく周波数制御を開始する構成とすることができる。つまり、走査光が走査方向の形成開始位置より所定距離だけ上流側の位置に到達すると周波数情報に基づく周波数制御を開始する構成とすることができる。 In the present embodiment, as shown in FIG. 9, the reference frequency corresponding to each sheet is matched with the frequency of the clock signal at the formation start position of each sheet indicated by the frequency information. Then, as shown in FIG. 10A, the image signal generation unit 203 generates a clock signal having a reference frequency until the scanning light reaches the formation start position 50. After the scanning light reaches the latent image formation start position, the image signal generation unit 203 controls the frequency of the clock signal so as to be the frequency indicated by the frequency information while the latent image is formed. After the scanning light arrives at the position where the latent image is formed, the image signal generation unit 203 generates a clock signal having a reference frequency. Since the formation start position is counted by the clock signal of the reference frequency, the writing position can be maintained with high accuracy without causing a correction residual. Further, as shown in FIG. 9, the section boundary in the frequency information can be provided so as to coincide with the end portion of the latent image forming region of the sheet in the scanning direction. As a result, the reference frequency matches the frequency for correcting the fluctuation of the scanning speed at the latent image formation start position of the sheet to be image-formed, and thus the accuracy of the latent image formation start position can be further improved. can. If an electrical delay occurs at the start of control that changes the frequency of the clock signal according to the image height according to the frequency information, the frequency information is input from a little before the timing when the scanning light reaches the formation start position. It can be configured to start frequency control based on. That is, the frequency control based on the frequency information can be started when the scanning light reaches a position on the upstream side by a predetermined distance from the formation start position in the scanning direction.

なお、本実施形態では、シートのサイズにより潜像の形成開始位置が定まり、かつ、基準周波数を、周波数情報が示す形成開始位置における周波数としたが、以下に説明する様に、本発明はそのような形態に限定されない。例えば、潜像の形成開始位置を、ユーザが設定した余白を含めて定義する場合を考える。つまり、潜像の形成領域とは、ユーザが設定した余白の領域を含まないものとする場合を考える。この場合、潜像の形成開始位置は、シートのサイズと、ユーザが設定した余白により決定されることになり、様々な位置となり得る。したがって、基準周波数をシートのサイズに応じて予め設定した複数の基準周波数から選択する場合、基準周波数と周波数情報が示す形成開始位置における周波数とを一致させることができない。 In the present embodiment, the formation start position of the latent image is determined by the size of the sheet, and the reference frequency is set to the frequency at the formation start position indicated by the frequency information. It is not limited to such a form. For example, consider the case where the formation start position of the latent image is defined including the margin set by the user. That is, consider the case where the latent image forming region does not include the margin region set by the user. In this case, the position where the latent image is formed is determined by the size of the sheet and the margin set by the user, and can be various positions. Therefore, when the reference frequency is selected from a plurality of reference frequencies set in advance according to the size of the sheet, the reference frequency and the frequency at the formation start position indicated by the frequency information cannot be matched.

この場合、周波数情報が示す形成開始位置における周波数に最も近い基準周波数を複数の基準周波数から選択する。図１０（Ｂ）は、周波数情報が示す形成開始位置における周波数と基準周波数とが異なる場合における、基準周波数から周波数情報が示す周波数の切替方法を示している。図１０（Ｂ）において、選択した基準周波数に対応する像高の位置を基準位置５１と呼ぶものとする。図１０（Ｂ）に示す様に、基準位置５１は、形成開始位置５０よりも走査方向において上流側の位置である。画像信号生成部２０３は、走査光が基準位置５１に到達するまでは基準周波数のクロック信号を発生し、走査光が基準位置に達すると、当該走査線における潜像の形成が完了するまでは、周波数情報に従いクロック信号の周波数を制御する。画像信号生成部２０３は、形成開始位置に到達するタイミングを、クロック信号の周波数、つまり、基準位置までは基準周波数であり、基準位置から形成開始位置までは周波数情報に基づく周波数であるクロック信号の周波数によりカウントする。したがって、形成開始位置には補正残差が生じるが、従来の様な１つの基準周波数とは異なり、複数の基準周波数から、周波数情報が示す形成開始位置における周波数に最も近い周波数を選択しているため、補正残差を小さくすることができる。なお、周波数情報に従い、像高に応じてクロック信号の周波数を変化させる制御の開始時に電気的な遅延が発生する場合には、走査光が基準位置に到達するタイミングより少し前から周波数情報に基づく周波数制御を開始する構成とすることができる。つまり、走査光が基準位置より所定距離だけ上流側の位置に到達すると周波数情報に基づく周波数制御を開始する構成とすることができる。また、複数の基準周波数から基準周波数を選択するのではなく、周波数情報が示す形成開始位置における周波数に基づき画像信号生成部２０３が基準周波数を決定する場合であっても、基準周波数を当該形成開始位置における周波数とは異ならせる構成とすることもできる。上述したのと同じ理由により、基準周波数と、周波数情報が示す形成開始位置における周波数との誤差を閾値以内とすることで、補正残差を小さくすることができる。なお、基準位置は、図１０（Ｂ）に示す様に、潜像の形成開始位置より感光体１０３の走査方向において上流側の位置とする。例えば、基準位置は、潜像の形成開始位置と、当該形成開始位置より走査方向の上流側であり、かつ、最も近い境界との間の位置とすることができる。或いは、基準位置を形成開始位置より走査方向の上流側であり、かつ、最も近い境界の位置とすることができる。 In this case, the reference frequency closest to the frequency at the formation start position indicated by the frequency information is selected from a plurality of reference frequencies. FIG. 10B shows a method of switching the frequency indicated by the frequency information from the reference frequency when the frequency at the formation start position indicated by the frequency information and the reference frequency are different. In FIG. 10B, the position of the image height corresponding to the selected reference frequency is referred to as the reference position 51. As shown in FIG. 10B, the reference position 51 is a position on the upstream side in the scanning direction from the formation start position 50. The image signal generation unit 203 generates a clock signal having a reference frequency until the scanning light reaches the reference position 51, and when the scanning light reaches the reference position, until the formation of the latent image on the scanning line is completed. The frequency of the clock signal is controlled according to the frequency information. The image signal generation unit 203 sets the timing of reaching the formation start position of the clock signal frequency, that is, the reference frequency up to the reference position and the frequency based on the frequency information from the reference position to the formation start position. Count by frequency. Therefore, although a correction residual is generated at the formation start position, unlike the conventional one reference frequency, the frequency closest to the frequency at the formation start position indicated by the frequency information is selected from a plurality of reference frequencies. Therefore, the correction residual can be reduced. If an electrical delay occurs at the start of control that changes the frequency of the clock signal according to the image height according to the frequency information, it is based on the frequency information from a little before the timing when the scanning light reaches the reference position. It can be configured to start frequency control. That is, the frequency control based on the frequency information can be started when the scanning light reaches a position on the upstream side by a predetermined distance from the reference position. Further, even when the image signal generation unit 203 determines the reference frequency based on the frequency at the formation start position indicated by the frequency information instead of selecting the reference frequency from a plurality of reference frequencies, the formation start of the reference frequency is performed. It can also be configured to be different from the frequency at the position. For the same reason as described above, the correction residual can be reduced by keeping the error between the reference frequency and the frequency at the formation start position indicated by the frequency information within the threshold value. As shown in FIG. 10B, the reference position is a position upstream of the latent image formation start position in the scanning direction of the photoconductor 103. For example, the reference position can be a position between the formation start position of the latent image and the boundary upstream from the formation start position in the scanning direction and closest to the boundary. Alternatively, the reference position can be located on the upstream side in the scanning direction from the formation start position and at the position of the closest boundary.

この様に、画像形成に使用可能な総てのシートそれぞれについて基準周波数を設定しておく必要はない。基準情報にないサイズのシートについては、サイズの近いシートの基準周波数を選択して使用する。しかしながら、本実施形態では、複数の基準周波数から基準周波数を選択して使用するため、１つの基準周波数を使用する場合と比較して、基準周波数と形成開始位置において周波数情報が示す周波数との差が小さくなる。したがって、補正残差が小さくすることができ、潜像の形成開始位置の精度を高めることができる。また、周波数情報における区間境界を、シートの潜像形成領域の走査方向の端部に一致させなくとも、その距離が短ければ従来手法に比べて形成開始位置の精度を高めることができる。また、シートのサイズとユーザが設定する余白量に基づき潜像の形成開始位置を決定する場合、周波数情報が示す当該形成開始位置に対応する像高における周波数、或いは、当該周波数との差が閾値以内である周波数を基準周波数として選択する。或いは、当該形成開始位置から、周波数情報が示す区間の上流側の境界までの位置から基準位置を選択し、周波数情報が示す当該基準位置での周波数を基準周波数とすることもできる。さらに、１つのシート内において複数の余白設定があり、ライン毎に形成開始位置が異なる場合においてはライン単位で基準周波数を変化させることができる。なお、本実施形態では、周波数情報の区間を９つとしたが、例示であり、他の区間数であっても良い。 In this way, it is not necessary to set a reference frequency for each of the sheets that can be used for image formation. For sheets with a size that is not included in the reference information, select and use the reference frequency for sheets that are close in size. However, in the present embodiment, since the reference frequency is selected from a plurality of reference frequencies and used, the difference between the reference frequency and the frequency indicated by the frequency information at the formation start position is compared with the case where one reference frequency is used. Becomes smaller. Therefore, the correction residual can be reduced, and the accuracy of the latent image formation start position can be improved. Further, even if the section boundary in the frequency information does not coincide with the edge of the latent image forming region of the sheet in the scanning direction, if the distance is short, the accuracy of the forming start position can be improved as compared with the conventional method. When the latent image formation start position is determined based on the sheet size and the margin amount set by the user, the frequency at the image height corresponding to the formation start position indicated by the frequency information or the difference from the frequency is the threshold value. A frequency within is selected as the reference frequency. Alternatively, the reference position can be selected from the position from the formation start position to the boundary on the upstream side of the section indicated by the frequency information, and the frequency at the reference position indicated by the frequency information can be used as the reference frequency. Further, when there are a plurality of margin settings in one sheet and the formation start position is different for each line, the reference frequency can be changed for each line. In the present embodiment, the frequency information section is set to 9, but this is an example, and the number of sections may be other.

［その他の実施形態］
本発明は、上述の実施形態の１以上の機能を実現するプログラムを、ネットワーク又は記憶媒体を介してシステム又は装置に供給し、そのシステム又は装置のコンピュータにおける１つ以上のプロセッサーがプログラムを読出し実行する処理でも実現可能である。また、１以上の機能を実現する回路（例えば、ＡＳＩＣ）によっても実現可能である。 [Other Embodiments]
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

１０３：感光体、１１２：光源、１１５：回転多面鏡、１１７：走査レンズ、２０３：画像信号生成部、２０５：記憶部 103: Photoreceptor, 112: Light source, 115: Rotating multifaceted mirror, 117: Scanning lens, 203: Image signal generator, 205: Storage unit

Claims

Photoreceptor and
A generation means for generating a clock signal and
A light source driven based on image data corresponding to the clock signal generated by the generation means, and
A deflection means for deflecting the light emitted by the light source to scan the photoconductor in order to form a latent image corresponding to the image data on the photoconductor, and the scanning speed of the light for scanning the photoconductor. With the deflection means, which changes according to the image height,
A determination means for determining the formation start position of the latent image formed on the photoconductor, and
A control means for controlling the frequency of the clock signal generated by the generation means, and
Is equipped with
The control means controls the frequency of the clock signal so as to be a reference frequency determined according to the formation start position at the first position on the upstream side of the formation start position in scanning one scanning line. Then, at the second position for forming the latent image corresponding to the image data on the downstream side of the formation start position, the relationship between the image height of the photoconductor and the frequency of the clock signal generated by the generation means. The frequency of the clock signal is controlled so as to be the frequency indicated by the frequency information indicating
The control means is an image forming apparatus, characterized in that the reference frequency is determined based on the frequency of the image height corresponding to the formation start position indicated by the frequency information.

The image according to claim 1, wherein the control means fixes the frequency of the clock signal to the reference frequency until the light deflected by the deflection means reaches the first position. Forming device.

The control means 1 or 2 is characterized in that the control means determines the timing at which the light deflected by the deflection means reaches the formation start position based on the frequency of the clock signal generated by the generation means. The image forming apparatus according to.

The image forming apparatus according to any one of claims 1 to 3, wherein the reference frequency is equal to the frequency of the image height corresponding to the formation start position indicated by the frequency information.

The determination means determines the formation end position of the latent image formed on the photoconductor, and determines the position where the latent image is formed.
1. The control means is characterized in that, in scanning one scanning line, the frequency of the clock signal is controlled so as to be the reference frequency at a third position downstream from the formation end position. 4. The image forming apparatus according to any one of 4.

Photoreceptor and
A generation means for generating a clock signal and
A light source driven based on image data corresponding to the clock signal generated by the generation means, and
A deflection means for deflecting the light emitted by the light source to scan the photoconductor in order to form a latent image corresponding to the image data on the photoconductor, and the scanning speed of the light for scanning the photoconductor. With the deflection means, which changes according to the image height,
A determination means for determining the formation start position of the latent image formed on the photoconductor, and
A control means for controlling the frequency of the clock signal generated by the generation means, and
Is equipped with
The control means determines a reference position from the formation start position or a position upstream of the formation start position in the scanning direction of the photoconductor, and determines the image height of the photoconductor and the clock generated by the generation means. Based on the frequency information indicating the relationship with the frequency of the signal, the reference frequency, which is the frequency of the image height corresponding to the reference position, is determined, and in scanning one scanning line, at the first position on the upstream side of the reference position. Is indicated by the frequency information at the second position for controlling the frequency of the clock signal so as to be the reference frequency and forming a latent image corresponding to the image data on the downstream side of the reference position. Control the frequency of the clock signal so that it becomes the frequency ,
An image forming apparatus, characterized in that the difference between the reference frequency and the frequency of the image height corresponding to the formation start position indicated by the frequency information is within a threshold value.

Photoreceptor and
A generation means for generating a clock signal and
A light source driven based on image data corresponding to the clock signal generated by the generation means, and
A deflection means for deflecting the light emitted by the light source to scan the photoconductor in order to form a latent image corresponding to the image data on the photoconductor, and the scanning speed of the light for scanning the photoconductor. With the deflection means, which changes according to the image height,
A determination means for determining the formation start position of the latent image formed on the photoconductor, and
A control means for controlling the frequency of the clock signal generated by the generation means, and
Is equipped with
The control means determines a reference position from the formation start position or a position upstream of the formation start position in the scanning direction of the photoconductor, and determines the image height of the photoconductor and the clock generated by the generation means. Based on the frequency information indicating the relationship with the frequency of the signal, the reference frequency, which is the frequency of the image height corresponding to the reference position, is determined, and in scanning one scanning line, at the first position on the upstream side of the reference position. Is indicated by the frequency information at the second position for controlling the frequency of the clock signal so as to be the reference frequency and forming a latent image corresponding to the image data on the downstream side of the reference position. Control the frequency of the clock signal so that it becomes the frequency,
The frequency information is provided for each of a plurality of sections arranged along the scanning direction of the photoconductor, and the frequency of each of the two ends of each section indicated by the frequency information in the scanning direction is the frequency of each of the two ends. The frequency that compensates for the change in scanning speed according to the image height of the above, and the frequency at a position different from the two ends of each section indicated by the frequency information is the change in scanning speed according to the image height at that position. Unlike the frequency that compensates for
The control means includes an end portion of the section indicated by the frequency information, which is upstream of the formation start position in the scanning direction and is closest to the formation start position, and the formation start position. images forming device from a position shall be the determining means determines said reference position between.

Photoreceptor and
A generation means for generating a clock signal and
A light source driven based on image data corresponding to the clock signal generated by the generation means, and
A deflection means for deflecting the light emitted by the light source to scan the photoconductor in order to form a latent image corresponding to the image data on the photoconductor, and the scanning speed of the light for scanning the photoconductor. With the deflection means, which changes according to the image height,
A determination means for determining the formation start position of the latent image formed on the photoconductor, and
A control means for controlling the frequency of the clock signal generated by the generation means, and
Is equipped with
The control means determines a reference position from the formation start position or a position upstream of the formation start position in the scanning direction of the photoconductor, and determines the image height of the photoconductor and the clock generated by the generation means. Based on the frequency information indicating the relationship with the frequency of the signal, the reference frequency, which is the frequency of the image height corresponding to the reference position, is determined, and in scanning one scanning line, at the first position on the upstream side of the reference position. Is indicated by the frequency information at the second position for controlling the frequency of the clock signal so as to be the reference frequency and forming a latent image corresponding to the image data on the downstream side of the reference position. Control the frequency of the clock signal so that it becomes the frequency,
The frequency information is provided for each of a plurality of sections arranged along the scanning direction of the photoconductor, and the frequency of each of the two ends of each section indicated by the frequency information in the scanning direction is the frequency of each of the two ends. The frequency that compensates for the change in scanning speed according to the image height of the above, and the frequency at a position different from the two ends of each section indicated by the frequency information is the change in scanning speed according to the image height at that position. Unlike the frequency that compensates for
The control means determines the position of the end portion of the section indicated by the frequency information, which is upstream of the formation start position in the scanning direction and is closest to the formation start position, as the reference position. images forming device you characterized by.

6. The image forming apparatus according to item 1.

The determination means determines the formation end position of the latent image formed on the photoconductor, and determines the position where the latent image is formed.
Wherein, in the scanning of one scanning line, according to claim 6 in a third position downstream of the forming end position, characterized in that for controlling the frequency of the clock signal so as to be the reference frequency 9. The image forming apparatus according to any one of 9.

The image forming apparatus according to any one of claims 1 to 10 , wherein the determination means determines the formation start position of the latent image based on the size of the sheet to be image-formed.

The image forming apparatus according to claim 11 , wherein the determination means determines the formation start position of the latent image based on a margin value set by a user.

Photoreceptor and
A generation means for generating a clock signal and
A light source driven based on image data corresponding to the clock signal generated by the generation means, and
A deflection means for deflecting the light emitted by the light source to scan the photoconductor in order to form a latent image corresponding to the image data on the photoconductor, and the scanning speed of the light for scanning the photoconductor. With the deflection means, which changes according to the image height,
Judgment means for determining the size of the sheet to be imaged,
A control means for controlling the frequency of the clock signal generated by the generation means, and
Is equipped with
The control means has a reference frequency determined according to the size of the sheet at the first position on the upstream side of the region determined according to the size of the sheet in scanning one scanning line. At the second position for controlling the frequency of the clock signal and forming a latent image corresponding to the image data in the region, the image height of the photoconductor and the frequency of the clock signal generated by the generation means are used. An image forming apparatus characterized in that the frequency of the clock signal is controlled so as to be the frequency indicated by the frequency information indicating the relationship with.

The image forming apparatus according to claim 13 , wherein the control means determines the reference frequency for each of the sizes of the plurality of sheets based on the reference information indicating the reference frequency.

The image formation according to claim 13 or 14 , wherein the control means determines a formation start position at which the latent image starts to be formed on the photoconductor based on the size of the sheet determined by the determination means. Device.

The frequency information is provided for each of a plurality of sections arranged along the scanning direction of the photoconductor.
The frequency of each of the two ends in the scanning direction of each section indicated by the frequency information is a frequency that compensates for a change in the scanning speed according to the image height of each of the two ends, and each of the frequencies indicated by the frequency information. The frequency at a position different from the two ends of the section is different from the frequency that compensates for the change in scanning speed according to the image height of the position.
A claim characterized in that the plurality of sections of the frequency information are provided so that the formation start position determined based on the size of the sheet coincides with the ends of the plurality of sections in the scanning direction. Item 15. The image forming apparatus according to item 15.

The image forming apparatus according to any one of claims 1 to 16 , further comprising a holding means for holding the frequency information.